1. Field of the Invention
The subject invention pertains to graft polymer polyols. More particularly, the subject invention pertains to new macromers suitable for the preparation of high solids, stable, low viscosity graft polymer polyol dispersions.
2. Description of the Related Art
A macromer is a polymer molecule with reactive functionality attached to it. The functionality allows the polymer to act as a high molecular weight monomer in another polymerization reaction. A common macromer strategy is to synthesize a polymer by polymerization of a monomer by one type of mechanism, and to include a small amount of a similar monomer. This second monomer has two reactive sites, one of which is capable of participating in the polymerization by the same mechanism. This second monomer also has a reactive site which is not capable of participating in the polymerization by the above mechanism, but is capable of reacting via a different mechanism.
An example of this might be a polymer made by condensation polymerization, e.g. a polyester. If one or more of the components of the polyester chain contain a group polymerizable a by free radical mechanism, e.g. an unsaturated dicarboxylic acid, then the polyester can serve as a monomer in a new polymer made by free radical polymerization. The use of unsaturated polyesters and styrene monomer to make fiberglass-reinforced plastics is well known.
A macromer is one of the key ingredients in the synthesis of graft polyols. It is a molecule with structure similar to the continuous phase of the product, i.e. a polyether or polyester polyol. In addition, it contains an unsaturated functionality which can undergo free radical polymerization with the vinylic monomers, to form the graft polymer. This graft polymer is the dispersion stabilizer which allows a stable graft polyol to be prepared. The resultant graft polyol is a stable dispersion of two incompatible materials. The part of the graft polymer which has structure similar to the acrylonitrile/styrene or other vinylic polymer dispersed phase associates with the copolymer, while the polyether component associates with the polyether continuous phase. The graft polymer is situated at the boundary between the two phases and ties them together.
Macromers, as herein defined, have been made since the late 60's and the synthesis and process for their manufacture is still basically the same: a polyether polyol or polyester polyol with hydroxyl termination is reacted under pressure with maleic anhydride and an excess of alkylene oxide. The maleic anhydride esterifies a hydroxyl group on the polyol, generating a carboxyl group in the process. The alkylene oxide can then react with the carboxyl group forming a hydroxyl-terminated ester, while at the same time, reducing the acid number of the macromer back to zero. The result is a polyether polyol with a site, the maleic acid moiety, capable of participating in the free radical-initiated polymerization of, for example, acrylonitrile and styrene. A typical process is disclosed in U.S. Pat. No. 3,953,393.
Over the years, as illustrated by U.S. Pat. No. 4,690,956, the basic synthesis has been changed to allow for an isomerization of maleate to fumarate to occur. Many base polyols have been used. A catalyst, generally a lipophilic calcium salt, has been used to promote the isomerization, lower the reaction temperature, and shorten the reaction time. But the same basic process, a "one step" batch-process in a pressure vessel, is still used today in production. Everything is charged in the beginning, the vessel sealed, and after reaction, the product is discharged. However, the reaction sequence is not just one step. There appear to be several competing reactions occurring, and as a result, the product is very sensitive to the conditions used to make it. This variability in the macromer from batch-to-batch has an effect of the quality of the graft polyols made with it.
Other macromers are known, which are used to make graft polyols, which do not use the maleate or fumarate moiety. An example is a macromer made by reacting a polyol with isocyantoethyl methacrylate. Macromers of this type are not storage-stable. They must be used immediately after synthesis or they soon increase in viscosity and become unusable.
It would be desirable to be able to prepare macromers containing ethylenic unsaturation in a more reproducible fashion, without the side reactions occurring during traditional macromer preparation. It would further be desirable to prepare macromers which are storage stable and which can be prepared in short cycle times without the use of a pressurized reactor.